The ciliate protozoan Tetrahymena pyriformis provides a good model system for the study of phospholipid biosynthesis in eukaryotes. The phospholipid compositon of the organism can be readily altered by inclusion of phospholipid base analogues in the growth medium whereas the phospholipid composition of mammalian cellular membranes is not easily modified. Using 2-aminoethylphosphonate (AEP) and 3-aminopropylphosphonate (APP) to modify the phospholipids of Tetrahymena, the uptake, incorporation into lipids and subsequent turnover of the normal phospholipid bases or precursors choline, ethanolamine, serine and methionine will be compared to those processes in normal cells to determine which enzymatic activities may have been altered by the abnormal phospholipid composition. Subsequently, the major enzymes of phospholipid biosynthesis (phosphatidylethanolamine-N-methyltransferase; phosphatidylserine synthetase and decarboxylase; diglyceride: CDP-choline, ethanolamine and CMP-AEP transferases) will be assayed in vitro to determine their activities in the lipid-altered cells relative to the normal. It is anticipated that such kinetic studies will lead to some understanding of the regulatory processes and interrelationships involved in phospholipid synthesis. The analogues of choline phosphate, N,N,N-trimethyl-AEP and N,N,N-trimethyl-APP will also be tested in vivo to determine if they can replace choline phosphate in the membrane phospholipids. AEP is a natural component of the phospholipids of Tetrahymena and many other organisms. Human exposure to AEP may come either from the diet (clams, oysters, etc.) or by infection (Mycobacterium tuberculosis) and AEP has been detected in human tissue on autopsy. Consequently, a study of the effect of the phosphoic acids on phospholipid metabolism in the model system can provide information which can be applied to mammalian phospholipid metabolism - both normal and abnormal.